The sampling of expired gases from breathing circuits in anesthesia is a well-known practice. It is desirable that the sample be taken as closely as possible to the patient's mouth piece. This helps to minimize mixing of the exhaled gases with inspired gases. It is also desirable to minimize the number of hoses that run from the patient to the respiratory machine. A reduction in the number of hoses that run to the patient, produces a corresponding reduction in the likelihood of having hoses become tangled or obstructed by torquing of the hoses.
U.S. Pat. No. 3,856,051 to Bane discloses a double lumen unilimb device where the inspired and expired air are contained within one limb that has an inner and outer hose. This design reduces the number of external hoses between the patient and the machinery from three tubes to two tubes if a sampling line is utilized and from four tubes to three tubes if a temperature probe or heater is also utilized. A unilimb design for respiratory hoses lowers heat loss to the patient. The reduction of heat loss occurs due to heat transfer between the exhaled and inhaled gases through the walls of the hoses in the unilimb. The unilimb design also reduces heat loss from heated inspired air because of the shielding by the warm outer expiratory tube.
U.S. Pat. No. 4,838,258 to Dryden et al. discloses a hose arrangement that includes a sampling hose contained inside one of two single lumen respiratory hoses. The other respiratory hose runs to the respirator as a single hose.
While the prior art has utilized double lumen unilimb hoses, several single-lumen hoses are still required with such unilimb hoses. Therefore, there remains a need to further reduce the number of lines between the patient and machine and to reduce the possibility of tangling and torquing of the breathing hoses. This may be accomplished according to my invention by providing a unilimb device that carries all of the required hoses or lines to the patient, the inspiratory gas hose, the expiratory gas hose, the sampling hose and any other required hoses or lines.
It is well-known that water vapor condensate interferes with analysis of gas samples that are taken from gas sampling hoses. The problem is created by the cooling of the moist exhaled gases from the patient, which causes water vapor to condense. Various types of water traps have been utilized to reduce the amount of condensate that reaches the gas analyzers. U.S. Pat. No. 4,717,403 to Choksi is an example of liquid traps utilized to prevent liquid condensation collection in gas analyzers. This device uses a separation chamber to separate the gas from the liquid. A liquid trap is an additional device to be placed in line prior to the gas analyzer to provide protection if an analyzer is to be utilized. Many liquid traps are not fully effective in preventing condensation from reaching gas analyzers. Provision must also be made for the emptying of condensate, for the trap to retain its effectiveness.
The patient on a respirator loses water as well as heat. I have determined that a device able to transfer the humidity from the expired air to the inspired air would reduce this moisture loss and decrease the problem of condensation from exhaled gases. The inspired air would also require less moisture to be added prior to inhalation by the patient and, therefore, less processing. A combination heat and humidity exchange device present in the patient end of the respiratory apparatus would be ideal for the patient and healthcare professional. Such a device that is able to separate gases from liquid condensate, and that also functions to exchange heat and moisture from expired air to the inspired air, and which is also part of the gas sampling device, is needed due to distinct advantages in terms of efficiency and simplicity of use. Such a device would reduce the need to heat and humidify inspired air and reduce the problems of handling collected condensates from the expired gas.
Mucus plugs are commonly encountered in respiratory devices, and frequently clog smaller hoses such as gas sampling hoses. These mucus plugs must be removed from the hose in order to obtain readings of gas composition from the sampling hose. I believe it is desirable to protect the sampling hose by preventing mucus from reaching it and thereby reduce the problems of mucus clogged hoses.
It would also be helpful to have a temperature sensor to measure the temperature of inspired gases after heat transfer from exhaled gases in the unilimb hose and heat transfer from the heat and moisture exchange media, to determine the degree of warming required for the inspired gases. The temperature may be determined by the use of a temperature probe in the region where the inhaled and exhaled gases mix.
Special connectors are desirable to incorporate my improvements and to allow compatibility with standard 15 and 22 mm respiratory connectors. Hoses for a unilimb breathing system may become twisted by torquing of the hose between the patient and machine. Therefore swivels which allow the remainder of the device to remain stationary while the hose connectors are free to rotate are helpful in order to eliminate torquing and to retain unobstructed airways. U.S. Pat. No. 4,967,744 to Chua utilizes one swivel in a swivel patient connector. While a single swivel allows rotation of the patient breathing device (mask, endotracheal tube) relative to the patient connector, the flexible breathing hose may still undergo torquing and may become obstructed unless, and according to one feature of my invention, at least one swivel and preferably two swivels are located in the patient adaptor (patient connector), one at each end, and at least one swivel is located on the machine end adaptor. These additional swivels according to my invention allow each end of the flexible breathing hose to rotate. The flexible breathing hose may rotate at the patient breathing device, the sampling adaptor or at the machine adaptor to prevent hose torquing.
In patient treatment, utilizing a breathing system, it is often necessary to vary the orientation of the patient end of the adaptor based on the relative position of the patient and the breathing means. In some instances, a 90.degree. elbow may be required between the adaptor and the breathing means (patient breathing mask or endotracheal tube), and in other instances, a straight connection is required. A patient end adaptor that is variable from a straight orientation to that of a 90.degree. bend is an improvement that I have incorporated to optimize the patient end adaptor orientation for each patient's use and to simplify installation of the apparatus because extra elbows or adaptors are no longer required.